The glycoproteins of animal cells are important constituents of the cell surface and intracellular organelles. Cell surface glycoproteins play a key role in the relationship of the cell to its environment. In addition, as components of the secretory and endocytic apparatus and as secretory products, glycoproteins are involved in the movement of compounds into and out of the cell. We plan to investigate two aspects of the close integration of glycoprotein function and metabolism, and the processes of secretion and endocytosis. First, we will study how sugar residues are transported out of the cytoplasm during the assembly of glycoprotein oligosaccharides. Results of these experiments should show how the synthetic apparatus is organized to ensure the correct final location of products, and the way in which cells establish and maintain surface properties. This project will extend our studies on the coupling between the synthesis and secretion of as paragine-linked oligosacchanides. Results should also be important in understanding the coupling between synthesis and secretion for many other macromolecular products in both prokaryotes and eukaryotes. Second, we will investigate the intracellular movements of receptor glycoproteins in receptor-medicated endocytosis. Experiments will seek to trace the path of receptor movement during the cycle of endocytosis and return to the cell surface. We plan to develop novel biochemical assays to spcifically test the passage of receptors and ligands through the lysosomal and Golgi compartments. Studies on transferrin, the plasma iron carrier, and its receptor in differentiating erythroid cells should furnish important information on the role of receptor movement in iron uptake and its control in these cells, and in the uptake of this important nutrient by all cells. These techniques will also be applicable to the study of receptors for peptide hormones, growth factors and lipoproteins, as well as receptors involved in the clearance of many proteins from plasma in understanding the role of endocytosis in cellular physiology.